1. Field of the Invention
The present invention relates to a phase-change optical information recording medium, which can be employed in optical memory appliances, more particularly to a phase-change optical information recording medium in the form of a rewritable compact disk, which is generally referred to as compact disk CD-RW.
2. Discussion of Background
As one of optical information memory media capable of recording information, reproducing recorded information and erasing the same with the application of magnetic waves such as laser beam thereto, the so-called phase-change optical information recording medium is known, which utilizes reversible phase changes from a crystalline state to an amorphous state and vice versa, or from one crystalline state to another crystalline state and vice versa.
Of such optical information memory media, the phase-change optical information recording media have been particularly subjected to vigorous research and development activities, since xe2x80x9coverwritexe2x80x9d, which would be extremely difficult to perform in the case of magneto-optical memory media, can be carried out by the phase-change optical information recording media with the application of a single beam thereto, and accordingly the optical system on a drive side for the phase-change optical information is simpler in mechanism than that for the magneto-optical memory media.
Conventionally, CDs (compact disks) have been recording media exclusively for reproducing for use with audio appliances or used as reproducing computer software. However, there have been placed on the market CD-Rewritable (usually abbreviated to CD-R), which is an optical information recording medium in which information can be recorded in the CD format, and CD-ReWritable (usually abbreviated to CD-RW), in which the above-mentioned phase-change material is employed, so that they find a variety of applications in the recording media for computers.
Previously, the standards for the phase-change optical recording media CD-RW (hereinafter simply referred to as DC-RW) were limited only to the recording at 2.4 to 2.8 m/s (2xc3x97line velocity recording), corresponding to double speed. As a matter of course, a long recording time is required at such a slow speed line velocity, so that there has been a demand for a rewritable CD capable of recording at much higher speed.
On the other hand, it has also been expected that CD-RW could be used as a 1xc3x97line velocity recording medium for use with audio appliances or the like.
In order to meet such various demands for recording applications, there have been demanded and in fact have been developed CD-RW media capable of performing multi-speed recording at a plurality of different line velocities on the same medium, namely, which are capable of performing recording at 2xc3x97line velocity and 4xc3x97line velocity, and also at 1xc3x97line velocity.
However, there is still a strong demand for further the enlargement of an effective range of the recording line velocities, and improvements, in particular, with respect to high quality recording at a low line velocity, and excellent compatibility with recording apparatus.
Furthermore, in the course of such various demands for recording applications, recently there has been developed a CD recorder for audio use. In accordance with the development of the CD recorder, there is increasing a demand for a recording medium which has high overwrite durability at low line velocity recording and is capable of attaining high quality recording.
Conventionally a storage capacity of 74 minutes or less has been mainly used. However, recently, CDs with a storage capacity of more than 74 minutes are increasing, which are for audio use. Under such circumstances, the demand for a recording medium with a larger storage capacity is increasing for backing up such long time recorded CDs.
In view of the above-mentioned status of the prior art in the field of this technology, a first object of the present invention is to provide a phase-change multi-speed optical information recording medium which is capable of recording at different line velocities, has excellent overwrite durability, with minimized reproduction errors, and which is also capable of attaining high quality signal recordings at low line velocities.
A second object of the present invention is to provide a phase-change multi-speed optical information recording medium which has a larger storage capacity than that in general use, namely, a larger memory capacity than that of a phase-change optical information recording CD-RW currently in general use.
By use of the phase-change multi-speed optical information recording medium of the present invention, an unconventionally effective recording method can be carried out at a low line velocity recording, with excellent durability to overwrite, and appropriate suitability for recording apparatus used in practice. Furthermore, in the present invention, the layer structure of the recording medium including a substrate structure is so optimized that the storage capacity is maximized.
The above-mentioned objects of the present invention can be achieved by a phase-change optical information recording medium which comprises a substrate and a recording layer provided on the substrate, the recording layer comprising a phase-change recording material capable of recording information, reproducing recorded information, and erasing recorded information reversibly with reversible phase changes in the phase-change recording material, with successive formation of a recording mark with a low reflectivity and a length of at least one unit extending in an optical recording scanning direction, and a space with a high reflectivity and a length of at least one unit extending in the optical recording scanning direction, wherein information is recorded by a plurality of signals being recorded in the recording layer, each signal constituting a recording mark area including a recording initiation marking portion with (a) a length of at least two times a minimum length of the recording mark and (b) a width (W1) of at least 1.1 times an average width (W2) of the other portion of the recording mark area.
In the above phase-change optical information recording medium, the space, when having a maximum length in terms of the unit, may have a signal level Itop, the recording initiation marking portion may have a signal level Ibtmf, and the other portion of the recording mark area may have a signal level Ibtme, which signal levels Itop, Ibtmf and Ibtme satisfy the formula I:
Itopxe2x88x92Ibtmfxe2x89xa7(Itopxe2x88x92Ibtme)
By the thus formed recording mark, recording can be attained with high quality signals with excellent overwrite durability.
Further, in the above phase-change optical information recording medium, the phase-change recording material for the recording layer may comprise constituent elements Ag, In, Sb, Te, and N or O, with the respective composition ratios xcex1, xcex2, xcex3, xcex4 and xcex5, in terms of atomic % being:
0 less than xcex1xe2x89xa610
3xe2x89xa6xcex2xe2x89xa615
50xe2x89xa6xcex3xe2x89xa665
20xe2x89xa6xcex4xe2x89xa635
0xe2x89xa6xcex5xe2x89xa610, wherein xcex1+xcex2+xcex3+xcex4+xcex5=100.
By the provision of the recording layer with the above-mentioned composition, signal recording performance at low line velocity can be further improved, and the compatibility of this recording medium with other recording apparatus and the range of the corresponding line velocities can be significantly enlarged.
In the above-mentioned phase-change optical information recording medium, the information can be recorded in the phase-change recording material with a different recording line velocity which is either a high recording line velocity or a low recording line velocity, the high recording line velocity being at least 1.2 times the low recording line velocity, the low recording line velocity being any of (1) 1.2 m/s to 1.4 m/s, (2) 2.4 m/s to 2.8 m/s, or (3) 4.8 m/s to 5.6 m/s.
By the above-mentioned recording line velocities, high quality recording at low line velocity can be attained, while maintaining the compatibility with conventional CD-RW recording apparatus. Furthermore, the range of the recording velocity corresponding to the CD-RW can be enlarged.
Further, in the above-mentioned phase-change optical information recording medium, the phase-change optical information recording medium may be in the shape of a disk, including a disk-shaped signal recordable area with a diameter of 120 mm or less, which is rotatable round a central rotation axis, with a difference between (1) a displacement in the vertical direction of the central rotation axis of an innermost circumference of the disk-shaped signal recordable area and (2) a displacement in the vertical direction of the central rotation axis of an outermost circumference of the disk-shaped signal recordable area being in a range of 10 xcexcm to 160 xcexcm.
Further, in the above-mentioned phase-change optical information recording medium, the phase-change optical information recording medium may be in the shape of a disk, including a disk-shaped signal recordable area with a diameter of 120 mm or less, which is rotatable round a central rotation axis, wherein when there is formed a TILT angle (xcex81) is formed between (1) a flat surface which is positioned with a right angle with respect to the central rotation axis, passing through an inner tangent point on one external surface of the disk-shaped recording medium, which inner tangent point corresponds to a point at the innermost circumference of the disk-shaped signal recordable area, and (2) a tangent at the inner tangent point externally directed in a radius direction of the disk-shaped recording medium, and also when there is formed a TILT angle (xcex82) is formed between (1) the flat surface and (3) a tangent at an outer tangent point, which outer tangent point corresponds to a point at the outermost circumference of the disk-shaped signal recordable area, externally directed in the same radius direction as mentioned above of the disk-shaped recording medium, it is preferable that an average difference between the TILT angle (xcex81) and the TILT angle (xcex82) be in a range of xe2x88x920.050xc2x0 to 0.320xc2x0, provided at least one of the TILT angle (xcex81) or the TILT angle (xcex82) may also be at zero.
By the above-mentioned mechanical characteristics of the phase-change optical information recording medium, the recording and reproducing suitability of the recording medium for currently commercially available recording apparatus can be improved, and recording can be performed with high quality signals.
Further, in the above-mentioned phase-change optical information recording medium, it is preferable that the substrate comprise guide grooves with a pitch having a pitch of 1.43xc2x10.3 xcexcm for recording signals in the phase-change recording material.
Further, in the above-mentioned phase-change optical information recording medium, it is preferable that the disk-shaped recording medium have a read-in radius in a range of 45.6 mm to 46.2 mm, and a read-out radius of 116.2 mm or less.
By the formation of the above-mentioned guide grooves, the storage capacity of the phase-change optical information recording medium can be significantly increased, and also the recording and reproducing suitability of the recording medium for currently commercially available recording apparatus can be secured.
Further, in the above-mentioned phase-change optical information recording medium, it is preferable that the substrate comprise guide grooves with a depth of 180 xc3x85 to 250 xc3x85 for recording signals in the phase-change recording material.
By the above depth of the guide grooves, the storage capacity of the recording medium can be increased, and the deterioration of signals can be prevented.
Further, in the above-mentioned phase-change optical information recording medium, it is preferable that the substrate further comprise guide grooves for recording signals in the phase-change recording material, and that the recording medium further comprise a first protective layer on the substrate, on which first protective layer, there are successively overlaid the recording layer, a second protective layer and a reflection layer, and that the recording layer have a thickness of 180 xc3x85 to 250 xc3x85.
By the provision of the recording layer with the above thickness, excellent recording and reproducing performance can be attained at low line velocity recording by use of the currently employed recording and reproducing apparatus.
In the above-mentioned phase-change optical information recording medium, it is preferable that the information be recorded in the phase-change recording material with a different recording line velocity which is either a high recording line velocity or a low recording line velocity, the recording with the low recording line velocity being carried out with such a ratio of an erasing power Pel to a recording power Pwl, that is, Pel/Pwl, being smaller than a ratio of an erasing power Peh to a recording power Pwh, that is, Peh/Pwh, at the time of recording carried out with the high recording line velocity.
Finally, in the above-mentioned phase-change optical information recording medium, it is preferable that the ratio of Pel/Pwl at the low recording line velocity be in the range of 0.3 to 0.5 (0.3xe2x89xa6Pel/Pwlxe2x89xa60.5).
By setting the ratio of Pel/Pwl at the low line velocity as mentioned above and also by making the ratio of Peh/Pwh smaller than the ratio of Pel/Pwl, the remaining heat in the erased area can be reduced and appropriate mark recording can be attained. As a result, the signal characteristics at low line recording velocity can be improved. Furthermore, excess laser power is not applied to the recording medium, the overwrite characteristics can be appropriately maintained or improved.